The method and apparatus according to the invention is different from the systems generally known as "automatic drive", which include a gearbox especially designed for automation, such as, for instance, a box with epicycloidal gears, provided with electromagnetic brakes or clutches, and associated with a torque converter or hydraulic coupling means. On the contrary, the present invention aims at automatizing a gearbox of conventional type, the changes in reduction ratios of which are obtained by shifting dogs which are generally controlled by sliding forks.